Synopsis

Diffusion weighted imaging showed the potential
to evaluate thyroid disease. This study aimed to evaluate whether readout-segmented
EPI (RS-EPI) can provide better image quality in imaging thyroid gland in
comparison with single-shot EPI (SS-EPI), and to compare ADC values, acquired
from RS-EPI with those of SS-EPI. Sixteen patients were examined using both
techniques. There were significant differences in susceptibility, motion
artifacts, except for detectability of thyroid nodules and ADC measurements
between RS-EPI and SS-EPI. The present study found that the RS-EPI technique
provides significant image quality improvement compared with SS-EPI in imaging thyroid
gland at 3 Tesla.

Purpose

Thyroid nodule is a common disorder of the
thyroid gland [1]. Several studies have been reported that apparent diffusion
coefficient (ADC) values can discriminate benign and malignant thyroid nodules [2-4].
Single-shot echo planar imaging (SS-EPI) is the most frequently used technique
because of its relative insensitive to motion-induced phase errors, high
signal-to-noise ratio and short acquisition times [5]. However, SS-EPI images
are characterized by blurring along the phase encoding direction due to T2*
decay and are sensitive to off-resonance effects [6], especially
in the neck area. Recently, a novel multi-shot technique, called readout-segmented
echo planar imaging (RS-EPI), has been proposed to improve the spatial
resolution , decrease the susceptibility based image distortion and T2*
blurring and a robust correction for motion-induced phase artifact [7]. We
hypothesized and believed that the RS-EPI could have a promising application
for diffusion weighted imaging (DWI) in thyroid gland, which is complex and
prone to severe artefacts. Therefore, the aims of the present study are twofold,
to evaluate whether RS-EPI can provide better image quality in imaging thyroid
gland in comparison with SS-EPI, and to compare ADC values, acquired from RS-EPI
with those of SS-EPI.

Materials and Methods

Subjects Sixteen patients (age, 45.8±16.8 years; male/female, 3/13) with thyroid
disease were enrolled in this prospective study, which was approved by the local
institutional review board and written informed consent was obtained from each
patient. MRI protocols Magnetic
resonance imaging was performed on a 3T MR system (Skyra, Siemens medical
solution, Germany) using a standard 20-channel phased-array head/neck coil. In
all patients, the examination protocols of thyroid gland included an axial
T1-weighted turbo spin-echo (T1W TSE), a coronal T2-weighted TSE and two axial DWI
with RS-EPI and SS-EPI techniques. T1W and T2W images were used for detecting
the thyroid nodules and positioning the DWI sequences. The parameters of these
protocols were summarized in Table 1. The total scan time of each subject was
approximately 10 minutes. Image analysis RS-EPI and SS-EPI DWI images were evaluated by two
independent observers (with 4 and 6 years of experience, respectively) for
identification of susceptibility, motion artifacts (1, marked; 3, no artifact)
and detectability of thyroid nodules (1, poor; 3, good) using quantitative
scores. ADC values of thyroid nodules were measured and
compared. The regions of interest (ROI) of thyroid nodules were manually
outlined on ADC maps with the sizes of ROIs ranged from 1.05 mm2 to
4.2 mm2. Statistical analysis Significant differences between RS-EPI
and SS-EPI for visual scores, and ADC value were assessed by using Wilcoxon
signed rank tests.

Discussion and Conclusion

In
this study, we demonstrated significantly higher image quality of thyroid DWI
using RS-EPI than that using the conventional SS-EPI technique, with no significant
difference in ADC values, which indicated that RS-EPI DWI is an effective method
for reducing image distortion, artefacts and improving image quality in thyroid
gland. The distortion in DWI was significantly reduced with RS-EPI. The RS-EPI
technique provides significant image quality improvement compared with SS-EPI
at 3 Tesla, and can potentially offer high image quality in imaging thyroid
gland.